Magical item

A magical item or magical object is an item which when polymorphed, has a tendency to become another magical item of the same type. Junk magical items can therefore be polypiled to produce other magical items.

Unicorn horns are a special case in NetHack 3.6.0: they are magical items by default and most horns you find can be polypiled into other magical tools. However, unicorn horns that are "regrown"—dropped by a unicorn that has been revived at least once—are treated as non-magical items and will only polymorph into non-magical tools.